Date:	Wed, 13 Nov 2013 12:59:11 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Li Xi <pkuelelixi@...il.com>
Cc:	linux-ext4@...r.kernel.org, Shuichi Ihara <sihara@....com>
Subject: Re: Patch of adding utility to check the status of MMP

On Wed, Nov 13, 2013 at 08:07:35PM +0800, Li Xi wrote:
> Hi all,
> 
> MMP feature of ext4 really helps us a lot to avoid mounting file
> system more than once, especailly when using ext4 as the basis of a
> distributed file sytem, e.g. Lustre. However, lack of a userspace
> utility to check the status of MMP makes it diffcult to utilize this
> feature to make failover decisions. We tried to write a script to do
> so by parsing the output of debugfs command. But this solution is not
> very straight forward. In order to check the sequence and checksum
> correctly, the script has to embed a lot of value definition, which
> could be error prone.
> 
> Finally, we decided to add a new command in the e2fsprogs. With that
> command, a server is able to check the current MMP state of a device
> so that it can decide whether to take over the file system service
> from aother server. I think the patch might helps other use cases too.
> 
> The attachment is the patch.
> 
> Thanks,
> Li  Xi

Please add a signed-off-by line.

Also /me grumps about patch-as-attachment; inline is less cutting and pasting
for review. :)

> Index: e2fsprogs.git/e2fsprogs.spec.in
> ===================================================================
> --- e2fsprogs.git.orig/e2fsprogs.spec.in
> +++ e2fsprogs.git/e2fsprogs.spec.in
> @@ -132,6 +132,7 @@ exit 0
>  %{_root_sbindir}/mkfs.ext4dev
>  %{_root_sbindir}/resize2fs
>  %{_root_sbindir}/tune2fs
> +%{_root_sbindir}/mmpstatus
>  %{_sbindir}/filefrag
>  %{_sbindir}/mklost+found
>  %{_sbindir}/e2freefrag
> @@ -180,6 +181,7 @@ exit 0
>  %{_mandir}/man8/tune2fs.8*
>  %{_mandir}/man8/filefrag.8*
>  %{_mandir}/man8/e2freefrag.8*
> +%{_mandir}/man8/mmpstatus.8*
>  
>  %files devel
>  %defattr(-,root,root)
> Index: e2fsprogs.git/misc/mmpstatus.8.in
> ===================================================================
> --- /dev/null
> +++ e2fsprogs.git/misc/mmpstatus.8.in
> @@ -0,0 +1,56 @@
> +.\" -*- nroff -*-
> +.\" This file may be copied under the terms of the GNU Public License.
> +.\"
> +.TH MMPSTATUS 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
> +.SH NAME
> +mmpstatus \- Check MMP status of an ext4 file system
> +.SH SYNOPSIS
> +.B mmpstatus
> +[
> +.B \-c | \--check
> +]
> +[
> +.B \-n | \--nodename
> +]
> +.I [filesys]
> +.SH DESCRIPTION
> +.B mmpstatus
> +is used to check MMP status of an ext4 file system.
> +.I filesys
> +can be a device name (e.g.
> +.IR /dev/hdc1 ", " /dev/sdb2 ),
> +or an ext4 label or UUID specifier (e.g.
> +UUID=8868abf6-88c5-4a83-98b8-bfc24057f7bd or LABEL=root).
> +Normaly, the

"Normally" (there are several of these)

> +.B mmpstatus
> +program checks whether it is safe to mount the file system without taking
> +the risk of mounting it more than once.
> +.PP
> +MMP (multiple-mount protection) is a feature which protects
> +the file system from being mounted simultaneously to more than one node.
> +It is NOT safe to mount a file system when one of the following condition
> +is true:
> +.br
> +\	1. The MMP shows that fsck is running on the file system.
> +.br
> +\	2. The MMP are being updated by some node.
> +.br
> +The
> +.B mmpstatus
> +program might wait for some time to see whether MMP is updated by any node
> +during this period.
> +.PP
> +Normaly, The exit code returned by
> +.B mmpstatus
> +is 0 when it is safe to mount the filesystem, 1 when it is NOT safe to mount
> +the filesystem, and -1 on failure. When
> +.B \-i
> +flag is specified, the exit code
> +is 0 on success, -1 on failure.
> +.SH OPTIONS
> +.TP
> +.B \-i,
> +print out the MMP informantion rather than check it.

"information"

> +.SH SEE ALSO
> +.BR fstab (5),
> +.BR fsck (8),
> Index: e2fsprogs.git/misc/Makefile.in
> ===================================================================
> --- e2fsprogs.git.orig/misc/Makefile.in
> +++ e2fsprogs.git/misc/Makefile.in
> @@ -27,12 +27,12 @@ INSTALL = @INSTALL@
>  @BLKID_CMT@...DFS_MAN= findfs.8
>  
>  SPROGS=		mke2fs badblocks tune2fs dumpe2fs $(BLKID_PROG) logsave \
> -			$(E2IMAGE_PROG) @FSCK_PROG@ e2undo
> +			$(E2IMAGE_PROG) @FSCK_PROG@ @MMPSTATUS_PROG@ e2undo
>  USPROGS=	mklost+found filefrag e2freefrag $(UUIDD_PROG) $(E4DEFRAG_PROG)
>  SMANPAGES=	tune2fs.8 mklost+found.8 mke2fs.8 dumpe2fs.8 badblocks.8 \
>  			e2label.8 $(FINDFS_MAN) $(BLKID_MAN) $(E2IMAGE_MAN) \
>  			logsave.8 filefrag.8 e2freefrag.8 e2undo.8 \
> -			$(UUIDD_MAN) $(E4DEFRAG_MAN) @FSCK_MAN@
> +			$(UUIDD_MAN) $(E4DEFRAG_MAN) @FSCK_MAN@ @MMPSTATUS_MAN@
>  FMANPAGES=	mke2fs.conf.5
>  
>  UPROGS=		chattr lsattr @UUID_CMT@ uuidgen
> @@ -51,6 +51,7 @@ DUMPE2FS_OBJS=	dumpe2fs.o
>  BADBLOCKS_OBJS=	badblocks.o
>  E2IMAGE_OBJS=	e2image.o
>  FSCK_OBJS=	fsck.o base_device.o ismounted.o
> +MMPSTATUS_OBJS=	mmpstatus.o
>  BLKID_OBJS=	blkid.o
>  FILEFRAG_OBJS=	filefrag.o
>  E2UNDO_OBJS=  e2undo.o
> @@ -70,6 +71,7 @@ PROFILED_BADBLOCKS_OBJS=	profiled/badblo
>  PROFILED_E2IMAGE_OBJS=	profiled/e2image.o
>  PROFILED_FSCK_OBJS=	profiled/fsck.o profiled/base_device.o \
>  			profiled/ismounted.o
> +PROFILED_MMPSTATUS_OBJS=profiled/mmpstatus.o
>  PROFILED_BLKID_OBJS=	profiled/blkid.o
>  PROFILED_FILEFRAG_OBJS=	profiled/filefrag.o
>  PROFILED_E2FREEFRAG_OBJS= profiled/e2freefrag.o
> @@ -82,7 +84,8 @@ SRCS=	$(srcdir)/tune2fs.c $(srcdir)/mklo
>  		$(srcdir)/uuidgen.c $(srcdir)/blkid.c $(srcdir)/logsave.c \
>  		$(srcdir)/filefrag.c $(srcdir)/base_device.c \
>  		$(srcdir)/ismounted.c $(srcdir)/../e2fsck/profile.c \
> -		$(srcdir)/e2undo.c $(srcdir)/e2freefrag.c
> +		$(srcdir)/e2undo.c $(srcdir)/e2freefrag.c \
> +		$(srcdir)/mmpstatus.c
>  
>  LIBS= $(LIBEXT2FS) $(LIBCOM_ERR) 
>  DEPLIBS= $(LIBEXT2FS) $(DEPLIBCOM_ERR)
> @@ -300,6 +303,16 @@ fsck.profiled: $(FSCK_OBJS) $(PROFILED_D
>  	$(Q) $(CC) $(ALL_LDFLAGS) -g -pg -o fsck.profiled $(PROFILED_FSCK_OBJS) \
>  		$(PROFILED_LIBBLKID) $(LIBINTL)
>  
> +mmpstatus: $(MMPSTATUS_OBJS) $(DEPLIBBLKID)
> +	$(E) "	LD $@"
> +	$(Q) $(CC) $(ALL_LDFLAGS) -o mmpstatus $(MMPSTATUS_OBJS) $(LIBBLKID) \
> +		$(LIBINTL) $(LIBS)
> +
> +mmpstatus.profiled: $(MMPSTATUS_OBJS) $(PROFILED_DEPLIBBLKID)
> +	$(E) "	LD $@"
> +	$(Q) $(CC) $(ALL_LDFLAGS) -g -pg -o mmpstatus.profiled \
> +		$(PROFILED_MMPSTATUS_OBJS) $(PROFILED_LIBBLKID) $(LIBINTL)
> +
>  badblocks: $(BADBLOCKS_OBJS) $(DEPLIBS)
>  	$(E) "	LD $@"
>  	$(Q) $(CC) $(ALL_LDFLAGS) -o badblocks $(BADBLOCKS_OBJS) $(LIBS) $(LIBINTL)
> @@ -384,6 +397,10 @@ badblocks.8: $(DEP_SUBSTITUTE) $(srcdir)
>  	$(E) "	SUBST $@"
>  	$(Q) $(SUBSTITUTE_UPTIME) $(srcdir)/badblocks.8.in badblocks.8	
>  
> +mmpstatus.8: $(DEP_SUBSTITUTE) $(srcdir)/mmpstatus.8.in
> +	$(E) "	SUBST $@"
> +	$(Q) $(SUBSTITUTE_UPTIME) $(srcdir)/mmpstatus.8.in mmpstatus.8
> +
>  fsck.8: $(DEP_SUBSTITUTE) $(srcdir)/fsck.8.in
>  	$(E) "	SUBST $@"
>  	$(Q) $(SUBSTITUTE_UPTIME) $(srcdir)/fsck.8.in fsck.8 
> @@ -575,7 +592,8 @@ clean:
>  		e2undo.profiled mke2fs.profiled dumpe2fs.profiled \
>  		logsave.profiled filefrag.profiled uuidgen.profiled \
>  		uuidd.profiled e2image.profiled mke2fs.conf \
> -		profiled/*.o \#* *.s *.o *.a *~ core gmon.out
> +		mmpstatus.profiled profiled/*.o \#* *.s *.o *.a *~ core \
> +		gmon.out
>  
>  mostlyclean: clean
>  distclean: clean
> @@ -644,6 +662,9 @@ badblocks.o: $(srcdir)/badblocks.c $(top
>  fsck.o: $(srcdir)/fsck.c $(top_builddir)/lib/config.h \
>   $(top_builddir)/lib/dirpaths.h $(top_srcdir)/version.h \
>   $(srcdir)/nls-enable.h $(srcdir)/fsck.h
> +mmpstatus.o: $(srcdir)/mmpstatus.c $(top_builddir)/lib/config.h \
> + $(top_builddir)/lib/dirpaths.h $(top_srcdir)/version.h \
> + $(srcdir)/nls-enable.h $(top_srcdir)/lib/ext2fs/ext2fs.h
>  util.o: $(srcdir)/util.c $(top_builddir)/lib/config.h \
>   $(top_builddir)/lib/dirpaths.h $(top_srcdir)/lib/et/com_err.h \
>   $(top_srcdir)/lib/e2p/e2p.h $(top_srcdir)/lib/ext2fs/ext2_fs.h \
> Index: e2fsprogs.git/misc/mmpstatus.c
> ===================================================================
> --- /dev/null
> +++ e2fsprogs.git/misc/mmpstatus.c
> @@ -0,0 +1,120 @@
> +/*
> + * GPL HEADER START
> + *
> + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 only,
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License version 2 for more details (a copy is included
> + * in the LICENSE file that accompanied this code).
> + *
> + * You should have received a copy of the GNU General Public License
> + * version 2 along with this program; if not, write to the
> + * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> + * Boston, MA 021110-1307, USA
> + *
> + * GPL HEADER END
> + */
> +/*
> + * Copyright (C) 2013 DataDirect Networks, Inc.
> + */
> +
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <stdlib.h>
> +#include <assert.h>
> +#include <time.h>
> +#include <getopt.h>
> +#include <sys/time.h>
> +#include "ext2fs/ext2fs.h"
> +#include "blkid/blkid.h"
> +#include "../version.h"
> +#include "nls-enable.h"
> +
> +/*
> + * return 1 when MMP is being updated,
> + * 0 if not, and -1 on falure
> +*/
> +int main (int argc, char ** argv)
> +{
> +	char		*device;
> +	int		open_flags = 0;
> +	blk64_t		superblock = 0;
> +	blk64_t		blocksize = 0;
> +	ext2_filsys	filesystem = NULL;
> +	int		retval;
> +	const char	*usage =
> +		"usage: %s [-i] device";
> +	const char	*opt_string = "i";
> +	int c;
> +	int info = 0;
> +	const char *debug_prog_name = "mmpstatus";
> +
> +	add_error_table(&et_ext2_error_table);
> +	fprintf(stderr, "%s %s (%s)\n", debug_prog_name,
> +		E2FSPROGS_VERSION, E2FSPROGS_DATE);
> +	while ((c = getopt(argc, argv, opt_string)) != EOF) {

Probably fine to use the bare string "i" instead of opt_string here.

> +		switch (c) {
> +		case 'i':
> +			info++;
> +			break;
> +		default:
> +			com_err(argv[0], 0, usage, debug_prog_name);
> +			return -1;
> +		}
> +	}
> +
> +	if (optind != argc - 1) {
> +		com_err(argv[0], 0, usage, debug_prog_name);
> +		return -1;
> +	}
> +
> +	device = blkid_get_devname(NULL, argv[optind], NULL);
> +	if (device == NULL) {
> +		com_err(argv[0], 0, _("Unable to resolve '%s'"), device);
> +		return -1;
> +	}
> +
> +	retval = ext2fs_open(device, open_flags, superblock, blocksize,
> +	                  unix_io_manager, &filesystem);

You might want at least open_flags |= EXT2_FLAG_64BITS, because bigalloc FSes
require features that get turned on with that flag, and will fail the open call
if the flag isn't there.

Also I could whine about argument size mismatches for superblock and blocksize;
technically, both parameters are 32-bits yet the variables being passed in
are 64 bits.  Block size will never need 64 bits, and the ext2fs_open3() call
to fix superblock hasn't gone in yet.  Also, both variables are permanently
zero, so you could just open code them and let the compiler figure it out.

> +	if (retval) {
> +		com_err(argv[0], retval, _("while trying to open %s"),
> +			device);
> +		retval = -1;
> +		goto out_free_device;
> +	}
> +
> +	if (info) {
> +		retval = ext2fs_mmp_dump(filesystem);
> +		if (retval) {
> +			com_err(argv[0], retval, _("while trying to dump %s"),
> +				device);
> +		}
> +	} else {
> +		retval = ext2fs_mmp_start(filesystem);
> +		switch (retval) {
> +		case EXT2_ET_MMP_FAILED:
> +			com_err(argv[0], retval,
> +				_("while checking MMP status of %s"), device);
> +			retval = 1;
> +			break;
> +		case 0:
> +			com_err(argv[0], 0, "device '%s' is not used now\n",
> +				device);
> +			break;
> +		default:
> +			com_err(argv[0], retval,
> +				_("while checking MMP status of %s"), device);
> +			retval = -1;

Picking nits here, but 'break'?

> +		}
> +	}
> +	ext2fs_close(filesystem);
> +out_free_device:
> +	free(device);
> +	return retval;
> +}
> Index: e2fsprogs.git/configure.in
> ===================================================================
> --- e2fsprogs.git.orig/configure.in
> +++ e2fsprogs.git/configure.in
> @@ -718,6 +718,32 @@ esac]
>  AC_SUBST(FSCK_PROG)
>  AC_SUBST(FSCK_MAN)
>  dnl
> +dnl See whether to install the `mmpstatus' program
> +dnl
> +AC_ARG_ENABLE([mmpstatus],
> +[  --enable-mmpstatus           build mmpstatus program],
> +[if test "$enableval" = "no"
> +then
> +	MMPSTATUS_PROG='' MMPSTATUS_MAN=''
> +	AC_MSG_RESULT([Not building mmpstatus])
> +else
> +	MMPSTATUS_PROG=mmpstatus MMPSTATUS_MAN=mmpstatus.8
> +	AC_MSG_RESULT([Building mmpstatus])
> +fi]
> +,
> +[case "$host_os" in
> +  gnu*)
> +    MMPSTATUS_PROG='' MMPSTATUS_MAN=''
> +    AC_MSG_RESULT([Not mmpstatus by default])

"Not building mmpstatus"?

> +    ;;
> +  *)
> +    MMPSTATUS_PROG=mmpstatus MMPSTATUS_MAN=mmpstatus.8
> +    AC_MSG_RESULT([Building mmpstatus by default])
> +esac]
> +)
> +AC_SUBST(MMPSTATUS_PROG)
> +AC_SUBST(MMPSTATUS_MAN)
> +dnl
>  dnl See whether to install the `e2initrd-helper' program
>  dnl
>  AC_ARG_ENABLE([e2initrd-helper],
> Index: e2fsprogs.git/debugfs/debugfs.c
> ===================================================================
> --- e2fsprogs.git.orig/debugfs/debugfs.c
> +++ e2fsprogs.git/debugfs/debugfs.c
> @@ -2315,54 +2315,15 @@ try_again:
>  
>  void do_dump_mmp(int argc EXT2FS_ATTR((unused)), char *argv[])
>  {
> +	int retval;
>  #if CONFIG_MMP
> -	struct ext2_super_block *sb;
> -	struct mmp_struct *mmp_s;
> -	time_t t;
> -	errcode_t retval = 0;
> -
>  	if (check_fs_open(argv[0]))
>  		return;
> -
> -	sb  = current_fs->super;
> -	if (sb->s_mmp_block <= sb->s_first_data_block ||
> -	    sb->s_mmp_block >= ext2fs_blocks_count(sb)) {
> -		com_err(argv[0], EXT2_ET_MMP_BAD_BLOCK, "while dumping it.\n");
> -		return;
> -	}
> -
> -	if (current_fs->mmp_buf == NULL) {
> -		retval = ext2fs_get_mem(current_fs->blocksize,
> -					&current_fs->mmp_buf);
> -		if (retval) {
> -			com_err(argv[0], retval, "allocating MMP buffer.\n");
> -			return;
> -		}
> -	}
> -
> -	mmp_s = current_fs->mmp_buf;
> -
> -	retval = ext2fs_mmp_read(current_fs, current_fs->super->s_mmp_block,
> -				 current_fs->mmp_buf);
> -	if (retval) {
> -		com_err(argv[0], retval, "reading MMP block.\n");
> -		return;
> -	}
> -
> -	t = mmp_s->mmp_time;
> -	fprintf(stdout, "block_number: %llu\n", current_fs->super->s_mmp_block);
> -	fprintf(stdout, "update_interval: %d\n",
> -		current_fs->super->s_mmp_update_interval);
> -	fprintf(stdout, "check_interval: %d\n", mmp_s->mmp_check_interval);
> -	fprintf(stdout, "sequence: %08x\n", mmp_s->mmp_seq);
> -	fprintf(stdout, "time: %lld -- %s", mmp_s->mmp_time, ctime(&t));
> -	fprintf(stdout, "node_name: %s\n", mmp_s->mmp_nodename);
> -	fprintf(stdout, "device_name: %s\n", mmp_s->mmp_bdevname);
> -	fprintf(stdout, "magic: 0x%x\n", mmp_s->mmp_magic);
> -	fprintf(stdout, "checksum: 0x%08x\n", mmp_s->mmp_checksum);
> -#else
> -	fprintf(stdout, "MMP is unsupported, please recompile with "
> -	                "--enable-mmp\n");
> +#endif
> +	retval = ext2fs_mmp_dump(current_fs);
> +#if CONFIG_MMP
> +	if (retval)
> +		com_err(argv[0], retval, "while dumping it.\n");
>  #endif
>  }
>  
> Index: e2fsprogs.git/lib/ext2fs/ext2fs.h
> ===================================================================
> --- e2fsprogs.git.orig/lib/ext2fs/ext2fs.h
> +++ e2fsprogs.git/lib/ext2fs/ext2fs.h
> @@ -1468,6 +1468,7 @@ errcode_t ext2fs_symlink(ext2_filsys fs,
>  /* mmp.c */
>  errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf);
>  errcode_t ext2fs_mmp_write(ext2_filsys fs, blk64_t mmp_blk, void *buf);
> +errcode_t ext2fs_mmp_dump(ext2_filsys fs);
>  errcode_t ext2fs_mmp_clear(ext2_filsys fs);
>  errcode_t ext2fs_mmp_init(ext2_filsys fs);
>  errcode_t ext2fs_mmp_start(ext2_filsys fs);
> Index: e2fsprogs.git/lib/ext2fs/mmp.c
> ===================================================================
> --- e2fsprogs.git.orig/lib/ext2fs/mmp.c
> +++ e2fsprogs.git/lib/ext2fs/mmp.c
> @@ -19,7 +19,7 @@
>  #include <unistd.h>
>  #endif
>  #include <sys/time.h>
> -
> +#include <time.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <fcntl.h>
> @@ -259,6 +259,54 @@ out:
>  #endif
>  }
>  
> +errcode_t ext2fs_mmp_dump(ext2_filsys fs)
> +{
> +#ifdef CONFIG_MMP
> +	struct ext2_super_block *sb;
> +	struct mmp_struct *mmp_s;
> +	time_t t;
> +	errcode_t retval = 0;
> +
> +	sb  = fs->super;
> +	if (sb->s_mmp_block <= sb->s_first_data_block ||
> +	    sb->s_mmp_block >= ext2fs_blocks_count(sb)) {
> +		return EXT2_ET_MMP_BAD_BLOCK;
> +	}
> +
> +	if (fs->mmp_buf == NULL) {
> +		retval = ext2fs_get_mem(fs->blocksize,
> +					&fs->mmp_buf);
> +		if (retval)
> +			return retval;
> +	}
> +
> +	mmp_s = fs->mmp_buf;
> +
> +	retval = ext2fs_mmp_read(fs, fs->super->s_mmp_block,
> +				 fs->mmp_buf);
> +	if (retval)
> +		return retval;
> +
> +	t = mmp_s->mmp_time;
> +	fprintf(stdout, "block_number: %llu\n", fs->super->s_mmp_block);
> +	fprintf(stdout, "update_interval: %d\n",
> +		fs->super->s_mmp_update_interval);
> +	fprintf(stdout, "check_interval: %d\n", mmp_s->mmp_check_interval);
> +	fprintf(stdout, "sequence: %08x\n", mmp_s->mmp_seq);
> +	fprintf(stdout, "time: %lld -- %s", mmp_s->mmp_time, ctime(&t));
> +	fprintf(stdout, "node_name: %s\n", mmp_s->mmp_nodename);
> +	fprintf(stdout, "device_name: %s\n", mmp_s->mmp_bdevname);
> +	fprintf(stdout, "magic: 0x%x\n", mmp_s->mmp_magic);
> +	fprintf(stdout, "checksum: 0x%08x\n", mmp_s->mmp_checksum);
> +
> +	return 0;
> +#else
> +	fprintf(stdout, "MMP is unsupported, please recompile with "
> +	                "--enable-mmp\n");
> +	return EXT2_ET_OP_NOT_SUPPORTED;

I wonder, maybe this function should simply return the error code and let the
caller decide if it wants to print out an error?  (And, maybe do that on
stderr?)

<shrug> It's a matter of taste, though I'd rather my error messages show up
on stderr.

--D
> +#endif
> +}
> +
>  /*
>   * Make sure that the fs is not mounted or being fsck'ed while opening the fs.
>   */
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